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How do booklice avoid dessication?

How do booklice avoid dessication?


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I often find booklice (aka psocids) in old paper notes I have in semi-storage. These pages of paper are intentionally left in dry conditions on my desk to avoid damage. However, if the psocids live and feed totally within these pages, how are they getting any water? How do the booklice avoid drying out and dying?


SEED DEVELOPMENT | Onset of Desiccation Tolerance

Summary

Desiccation tolerance is established through a programed sequence of events during the later stages of seed development and is then lost progressively during subsequent germination. Tolerance is clearly a complex property involving mechanisms for cellular protection, and also for cellular repair during rehydration. Desiccation tolerance appears to be acquired in discrete water potential steps during development that have different water activities and associated metabolic processes, which may be related to specific desiccation stresses and discrete patterns of gene expression. Thus, the attainment of different levels of desiccation tolerance may be determined by progressive acquisition of specific tolerance mechanisms or by sufficient accumulation of desiccation protectants. Proteins such as the dehydrins appear to have a protective role and, at very low moisture contents, sugars may play a key protective role by functionally replacing water and thus stabilizing membranes and other sensitive systems.


Desiccation resistance in tropical insects: causes and mechanisms underlying variability in a Panama ant community

Desiccation resistance, the ability of an organism to reduce water loss, is an essential trait in arid habitats. Drought frequency in tropical regions is predicted to increase with climate change, and small ectotherms are often under a strong desiccation risk. We tested hypotheses regarding the underexplored desiccation potential of tropical insects. We measured desiccation resistance in 82 ant species from a Panama rainforest by recording the time ants can survive desiccation stress. Species' desiccation resistance ranged from 0.7 h to 97.9 h. We tested the desiccation adaptation hypothesis, which predicts higher desiccation resistance in habitats with higher vapor pressure deficit (VPD) - the drying power of the air. In a Panama rainforest, canopy microclimates averaged a VPD of 0.43 kPa, compared to a VPD of 0.05 kPa in the understory. Canopy ants averaged desiccation resistances 2.8 times higher than the understory ants. We tested a number of mechanisms to account for desiccation resistance. Smaller insects should desiccate faster given their higher surface area to volume ratio. Desiccation resistance increased with ant mass, and canopy ants averaged 16% heavier than the understory ants. A second way to increase desiccation resistance is to carry more water. Water content was on average 2.5% higher in canopy ants, but total water content was not a good predictor of ant desiccation resistance or critical thermal maximum (CT max), a measure of an ant's thermal tolerance. In canopy ants, desiccation resistance and CT max were inversely related, suggesting a tradeoff, while the two were positively correlated in understory ants. This is the first community level test of desiccation adaptation hypothesis in tropical insects. Tropical forests do contain desiccation-resistant species, and while we cannot predict those simply based on their body size, high levels of desiccation resistance are always associated with the tropical canopy.

Keywords: Body size CTmax VPD canopy thermal tolerance water content water loss.

Figures

Worker of Cephalotes atratus ,…

Worker of Cephalotes atratus , in a Dipteryx panamensis canopy next to the…


Silverfish and Firebrats

Silverfish (Figure 2) and firebrats (Figure 3) belong to a group of primitive insects called thysanura (thi?s?? nur ?). They are wingless and have slender, carrot-shaped bodies that are covered with scales. Both insects have two long slender antennae attached to their heads and three long tail-like appendages at the hind end. Each appendage is almost as long as the body. Adults are about 1/3 to 1/2 inch long (8 to 13 mm). Silverfish are shiny and silver or pearl-gray. Firebrats are mottled gray or brown.

Silverfish and firebrats are common in homes and can be found in places with high humidity and little airflow. They are active at night and hide during the day. When objects under which they hide are moved, they dart about seeking a new hiding place. Large numbers may be found in new buildings in which the newly plastered walls are still damp. Silverfish and firebrats may cause damage in the home by eating foods or other materials that are high in protein, sugar or starch. They eat cereals, moist wheat flour, paper on which there is glue or paste, sizing in paper and book bindings, starch in clothing, and rayon fabrics. In apartment buildings, the insects follow pipelines to rooms in search of food. They may be found in bookcases, around closet shelves, behind baseboards, or around windows or door frames.

Silverfish live and develop in damp, cool places. Firebrats live and develop in hot, dark places, such as around furnaces and fireplaces and in insulation around hot water or steam pipes.

Biology

Under normal house conditions, silverfish and firebrats develop slowly and have few young. Females lay eggs year-round in secluded places, such as behind books or on closet shelves however, occasionally they lay eggs in the open.

Silverfish lay only a few eggs at a time but may lay several batches over a period of weeks. The adult female can live for two to five years depending on the species, and can lay up to 100 eggs. The eggs are whitish, oval and about 1/32 inch long (0.8 mm). They hatch in two to eight weeks.

Firebrats lay about 50 eggs, one at a time, and will lay several batches. The adult female can live for about two years and can lay thousands of eggs. The eggs are soft, white, and opaque when they are laid. They later have a yellowish tinge. Firebrat eggs hatch in about two weeks.

After hatching, the young silverfish and firebrats look like the adults except they are smaller. Both insects reach maturity in three to 24 months. Their rate of growth depends on temperature and humidity.

Control

Sanitation can help prevent infestations but will not eliminate current infestations. Seal or remove hiding places. Sealing up cracks and crevices around plumbing, wall molding, and windowsills will help eliminate harborage (places for them to hide). Removing cardboard boxes and old newspapers eliminates food sources and harborage. Vacuuming can physically remove both silverfish and firebrats.

If insecticides are necessary, sprays should be applied to floors and wall moldings, behind drawers, under furniture, in cracks and crevices, and the floor and ceiling of attics. Outside, treat eaves, mulched flower beds, and storage sheds. Control may not be immediate because hiding insects must come out and contact spray residue. Dusts of the recommended materials may be used for treating walls, voids, crawl spaces, and attics. Ten days to two weeks may be required to determine whether or not control has been achieved. Space sprays of pyrethrins are useful for controlling exposed insects.


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FRONTIERS OF TOLERANCE

The two main applications of research on desiccation tolerance in the past two decades have been attempts to induce tolerance in human cells for medical purposes and to engineer tolerance in crop plants to make them less vulnerable to drought. Researchers have also tried to engineer or induce tolerance in agronomic bacteria and in nematodes used for biological control. Knowing what limits desiccation tolerance in prokaryotes and nematodes could also help control pathenogenic species that are naturally desiccation-tolerant ( Breeuwer et al., 2003). There has been considerable success in conferring tolerance on isolated membrances and enzymes and on single cells ( Billi and Potts, 2002 Crowe et al., 2005 Potts et al., 2005), which seems to accord with what we know about the inherent and phylogenetic limits of tolerance. There has been almost no success in crop plants, suggesting the importance of physical or physiological constraints on tolerance in whole, multicellular organisms.

Making single cells tolerate desiccation

Desiccation tolerance in mammalian cells can be induced by treatment with trehalose, a sugar accumulated during drying in many desiccation-tolerant animals. Whereas fresh human blood platelets have a shelf life of only about five days, platelets freeze-dried in a solution of trehalose can be stored much longer and then rehydrated for use ( Wolkers et al., 2001b, 2002). This technique specifically preserves membrane microdomains ( Crowe et al., 2003). Gordon et al. (2001) incubated human mesenchymal stem cells in 50 mmol trehalose and 3% glycerol, air-dried and stored them under vacuum, and express mailed them from San Diego to Baltimore, where they recovered normal morphology, lability, and regeneration capacity after rehydration. Incubation in a medium with a high trehalose concentration can make corneal epithelial cells desiccation-tolerant ( Matsuo, 2001). Chen et al. (2001) introduced trehalose into mammalian cells with an engineered protein that formed pores in the plasma membrane having about 10 10 molecules of trehalose per cell enabled cells to survive at 5% relative humidity and 20°C for weeks. There are now techniques to load human red blood cells with trehalose ( Satpathy et al., 2004). Under optimal conditions, sugar alone may suffice to make mammalian cells tolerate desiccation ( Crowe et al., 2002). Human cells can also tolerate desiccation in the absence of added sugars if dried slowly and stored under vacuum ( Puhlev et al., 2001).

Desiccation tolerance can be induced in the bacteria Escherichia coli and Pseudomonas putida with either trehalose or hydroectoine ( de Castro et al., 2000 Tunnacliffe et al., 2001 Manzanera et al., 2002, 2004). Loading the nitrogen-fixing mutualist bacterium Bradyrhizobium japonicum with trehalose by incubating it in the sugar during growth greatly improved its subsequent survival of desiccation, which is a major cause of failure of inoculation of leguminous crops with the bacterium in the field ( Streeter, 2003).

There has also been some success in engineering desiccation tolerance in mammalian cells and bacteria. Guo et al. (2000) used a recombinant adenovirus vector to express the otsA and otsB genes of Escherichia coli, which encode enzymes that synthesize trehalose, in human primary fibroblasts and were able to maintain infected cells in the dry state for up to five days. However, engineering mouse cells to produce 80 mmol trehalose did not make them fully desiccation-tolerant ( de Castro and Tunnacliffe, 2000), even when extracellular trehalose was supplied ( Tunnacliffe et al., 2001). Moving the spsA gene of a cyanobacterium into E. coli resulted in production of sucrose-6-phosphate synthetase and a 10,000-fold increase in survival of desiccation ( Billi et al., 2000). It is also possible to transfer genes into naturally tolerant cyanobacteria ( Billi et al., 2001), which might thereby become a desiccation-tolerant source of useful metabolites. Gene transfer may even have been significant in some natural origins of desiccation tolerance: the tolerant bacterium Dienococcus radiodurans appears to have acquired homologues of putative plant desiccation tolerance genes by horizontal transfer ( Makarova et al., 2001).

The success in making single cells tolerate desiccation fits with knowledge of the limits of tolerance. There seem to be no significant inherent limits on desiccation tolerance and no physical or physiological constraints that apply to single, non-rigid prokaryote or animal cells. If phylogeny limits tolerance in many animals via lack of available genetic variation for tolerance, then introducing genes for tolerance might be expected to successfully overcome this limit.

Making whole organisms tolerate desiccation

It has so far been possible to increase tolerance of partial desiccation in multicellular animals and plants, but not to make them desiccation-tolerant. Treatment with cold can increase production of trehalose and tolerance in nematodes used for biological control ( Grewal and Jagdale, 2002). Breeding can increase tolerance of partial desiccation to some extent in the entomopathogenic nematode Heterorhabditis bacteriophora ( Strauch et al., 2004). Introduction of trehalose biosynthetic genes into plants can increase their production of trehalose and their tolerance of various stresses but has not resulted in desiccation tolerance ( Penna, 2003). For example, regulated overexpression of genes from E. coli in rice plants increased their trehalose concentration 3–10 times ( Garg et al., 2002). The plants showed relatively low photooxidation and high ability to accumulate nutrients under salt, drought, or cold stress but did not tolerate desiccation.

Lack of success in making whole organisms tolerate desiccation may suggest that the known limits that apply to whole, multicellular organisms set major obstacles to engineering tolerance in them. For example, physical constraints in both animals and plants and physiological constraints due to involvement of hornones in tolerance in plants are likely to require more than just the engineering of synthesis of sugars to confer tolerance. To reduce mechanical stress, animals may need to contract during desiccation and plants need to have more flexible cell walls. Tolerance is unlikely to be engineered in plants taller than 3 m due to the problem of refilling xylem. What we know about the natural limits to desiccation tolerance in living things offers encouragement for further efforts to artificially extend tolerance to single-celled organisms and to individual cells and tissues of multicellular ones. However, we may need to know more about the limits of desiccation tolerance before we can expect to extend it to desiccation-sensitive whole plants and metazoans.

From the Symposium Drying Without Dying: The Comparative Mechanisms and Evolution of Desiccation Tolerance in Animals, Microbes, and Plants presented at the Annual Meeting of the Society for Integrative and Comparative Biology, 4–8 January 2005, at San Diego, California. Contribution no. 2242 from the University of California Bodega Marine Laboratory.

I thank the participants in the symposium on desiccation tolerance at the 2005 meeting of the Society for Integration and Comparative Biology for sharing their knowledge and insights.


Contents

Organisms that aestivate appear to be in a fairly "light" state of dormancy, as their physiological state can be rapidly reversed, and the organism can quickly return to a normal state. A study done on Otala lactea, a snail native to parts of Europe and Northern Africa, shows that they can wake from their dormant state within ten minutes of being introduced to a wetter environment.

The primary physiological and biochemical concerns for an aestivating animal are to conserve energy, retain water in the body, ration the use of stored energy, handle the nitrogenous end products, and stabilize bodily organs, cells, and macromolecules. This can be quite a task as hot temperatures and arid conditions may last for months. The depression of metabolic rate during aestivation causes a reduction in macromolecule synthesis and degradation. To stabilize the macromolecules, aestivators will enhance antioxidant defenses and elevate chaperone proteins. This is a widely used strategy across all forms of hypometabolism. These physiological and biochemical concerns appear to be the core elements of hypometabolism throughout the animal kingdom. In other words, animals which aestivate appear to go through nearly the same physiological processes as animals that hibernate. [2]

Mollusca Edit

Gastropoda: some air-breathing land snails, including species in the genera Helix, Cernuella, Theba, Helicella, Achatina and Otala, commonly aestivate during periods of heat. Some species move into shaded vegetation or rubble. Others climb up tall plants, including crop species as well as bushes and trees, and will also climb man-made structures such as posts, fences, etc.

Their habit of climbing vegetation to aestivate has caused more than one introduced snail species to be declared an agricultural nuisance.

To seal the opening to their shell to prevent water loss, pulmonate land snails secrete a membrane of dried mucus called an epiphragm. In certain species, such as Helix pomatia, this barrier is reinforced with calcium carbonate, and thus it superficially resembles an operculum, except that it has a tiny hole to allow some oxygen exchange. [ citation needed ]

There is a decrease in metabolic rate and reduced rate of water loss in aestivating snails like Rhagada tescorum, [3] Sphincterochila boissieri and others.

Arthropoda Edit

Insecta: Lady beetles (Coccinellidae) have been reported to aestivate. [4] Mosquitoes also are reported to undergo aestivation. [5] False honey ants are well known for being winter active and aestivate in temperate climates. Bogong moths will aestivate over the summer to avoid the heat and lack of food sources. [6] Adult alfalfa weevils (Hypera postica) aestivate during the summer in the southeastern United States, during which their metabolism, respiration, and nervous systems show a dampening of activity. [7] [8]

Crustacea: An example of a crustacean undergoing aestivation is with the Australian crab Austrothelphusa transversa , which undergoes aestivation underground during the dry season. [9]

Reptiles and amphibians Edit

Non-mammalian animals that aestivate include North American desert tortoises, crocodiles, and salamanders. Some amphibians (e.g. the cane toad and greater siren) aestivate during the hot dry season by moving underground where it is cooler and more humid. The California red-legged frog may aestivate to conserve energy when its food and water supply is low. [11]

The water-holding frog has an aestivation cycle. It buries itself in sandy ground in a secreted, water-tight mucus cocoon during periods of hot, dry weather. Australian Aboriginals discovered a means to take advantage of this by digging up one of these frogs and squeezing it, causing the frog to empty its bladder. This dilute urine—up to half a glassful—can be drunk. However, this will cause the death of the frog which will be unable to survive until the next rainy season without the water it had stored. [12]

The western swamp turtle aestivates to survive hot summers in the ephemeral swamps it lives in. It buries itself in various media which change depending on location and available substrates. [13] Because the species is critically endangered, the Perth Zoo began a conservation and breeding program for it. However, zookeepers were unaware of the importance of their aestivation cycle and during the first summer period would perform weekly checks on the animals. This repeated disturbance was detrimental to the health of the animals, with many losing significant weight and some dying. The zookeepers quickly changed their procedures and now leave their captive turtles undisturbed during their aestivation period.

Fish Edit

Mammals Edit

Although relatively uncommon, a small number of mammals aestivate. [16] Animal physiologist Kathrin Dausmann of Philipps University of Marburg, Germany, and coworkers presented evidence in a 2004 edition of Nature that the Malagasy fat-tailed dwarf lemur hibernates or aestivates in a small tree hole for seven months of the year. [17] According to the Oakland Zoo in California, four-toed hedgehogs are thought to aestivate during the dry season. [18]


The problem of size

Desiccation-tolerant animals may be small because of the physical stresses associated with drying (Table 2). Animal cells shrink as they dry, and the whole animal must shrink with them. All animals that tolerate desiccation as adults adopt distinctive, balled or curled shapes as they dry(Fig. 2). Rigid external or internal skeletons could prevent this, and none of these animals have skeletons. In the tolerant animals that do have exoskeletons, tolerance is restricted to juvenile stages before skeletons form(Fig. 3). It would be interesting to know whether there is generally a developmentally programmed acquisition and loss of tolerance at the cellular level in these animals, as there is in most seeds, or whether individual cells remain tolerant in some adult animals.

Problems caused by desiccation and mechanisms of desiccation tolerance

Problem . Mechanism . Selected references .
Mechanical damage due to shrinkage In plants, changes in cell wall composition that increase flexibility (Jones and McQueen-Mason,2004 Vicre et al.,2004b)
In plants, folding cell walls (Vander Willigen et al.,2004)
In plants, replacement of water in vacuoles by non-aqueous compounds and fragmentation of vacuoles (Farrant, 2000 Vicre et al., 2004a)
Physiological damage at low intermediate water contents Upregulation of proteins that increase membrane permeability (Smith-Espinoza et al., 2003 Vander Willigen et al., 2004)
Disintegration of membranes and aggregation of macromolecules during drying,coalescence of lipid bodies and membrane leakage upon rehydration Accumulation of sugars, especially non-reducing disaccharides, that stabilize molecules, depress temperature (Tm) of membrane phase change from liquid crystal to gel, and form glasses with high melting temperature (Tg) (Wingler, 2002 Bernacchia and Furini, 2004 Buitink and Leprince, 2004 Crowe et al., 2005)
LEA proteins, which act as molecular chaperones and interact with sugars to form glasses (Wise and Tunnacliffe, 2004 Goyal et al., 2005a Oliver et al., 2005)
Partitioning of amphiphiles into membranes (Hoekstra and Golovina, 2002 Oliver et al., 2002)
Small stress proteins, which may act as chaperones or repair damage upon rehydration (Collins and Clegg, 2004 Crowe et al., 2005 Potts et al., 2005)
Changes in lipid composition that stabilize membranes, such as increases in phospholipids, degree of saturation, and free sterols (Quartacci et al., 2002 Hoekstra, 2005)
In seeds, oleosins (Murphy, et al., 2001)
Generation of reactive oxygen species (ROS) Synthesis of antioxidants during drying, maintenance of pools of reduced antioxidants and ROS-scavenging enzymes (Shirkey et al., 2000 Augusti et al., 2001 Espindola et al., 2003 Kranner and Birtic, 2005)
In plants, downregulation of photosynthesis early in drying (Jensen et al., 1999 Deng et al., 2003 Hirai et al., 2004 Illing et al., 2005)
In plants, folding of leaves (Farrant et al., 2003)
Programmed chlorophyll loss (Tuba et al., 1996)
Triggering of cell death by oxidized glutathione Rapid reduction of glutathione upon rehydration (Kranner and Birtic, 2005)
In plants, disintegration of the photosynthetic apparatus Modification of proteins in PSII (Peeva and Maslenkova, 2004)
Accumulation of damage from UV and gamma radiation and from Maillard and Fenton reactions while dry UV-absorbing pigments (Potts, 1996)
DNA repair (Wilson et al., 2004)
DNA protection (Potts et al., 2005)
In plants, cavitation of xylem Height <3 m, low hydraulic conductivity (Sherwin et al., 1998)
Drying too fast for induction of tolerance mechanisms In animals, contraction, construction of larval tube by Polypedilum(Kikawada et al., 2005)
In plants, signaling for induction of tolerance mechanisms via ABA (Beckett et al., 2000 Bartels and Salamini, 2001)
Problem . Mechanism . Selected references .
Mechanical damage due to shrinkage In plants, changes in cell wall composition that increase flexibility (Jones and McQueen-Mason,2004 Vicre et al.,2004b)
In plants, folding cell walls (Vander Willigen et al.,2004)
In plants, replacement of water in vacuoles by non-aqueous compounds and fragmentation of vacuoles (Farrant, 2000 Vicre et al., 2004a)
Physiological damage at low intermediate water contents Upregulation of proteins that increase membrane permeability (Smith-Espinoza et al., 2003 Vander Willigen et al., 2004)
Disintegration of membranes and aggregation of macromolecules during drying,coalescence of lipid bodies and membrane leakage upon rehydration Accumulation of sugars, especially non-reducing disaccharides, that stabilize molecules, depress temperature (Tm) of membrane phase change from liquid crystal to gel, and form glasses with high melting temperature (Tg) (Wingler, 2002 Bernacchia and Furini, 2004 Buitink and Leprince, 2004 Crowe et al., 2005)
LEA proteins, which act as molecular chaperones and interact with sugars to form glasses (Wise and Tunnacliffe, 2004 Goyal et al., 2005a Oliver et al., 2005)
Partitioning of amphiphiles into membranes (Hoekstra and Golovina, 2002 Oliver et al., 2002)
Small stress proteins, which may act as chaperones or repair damage upon rehydration (Collins and Clegg, 2004 Crowe et al., 2005 Potts et al., 2005)
Changes in lipid composition that stabilize membranes, such as increases in phospholipids, degree of saturation, and free sterols (Quartacci et al., 2002 Hoekstra, 2005)
In seeds, oleosins (Murphy, et al., 2001)
Generation of reactive oxygen species (ROS) Synthesis of antioxidants during drying, maintenance of pools of reduced antioxidants and ROS-scavenging enzymes (Shirkey et al., 2000 Augusti et al., 2001 Espindola et al., 2003 Kranner and Birtic, 2005)
In plants, downregulation of photosynthesis early in drying (Jensen et al., 1999 Deng et al., 2003 Hirai et al., 2004 Illing et al., 2005)
In plants, folding of leaves (Farrant et al., 2003)
Programmed chlorophyll loss (Tuba et al., 1996)
Triggering of cell death by oxidized glutathione Rapid reduction of glutathione upon rehydration (Kranner and Birtic, 2005)
In plants, disintegration of the photosynthetic apparatus Modification of proteins in PSII (Peeva and Maslenkova, 2004)
Accumulation of damage from UV and gamma radiation and from Maillard and Fenton reactions while dry UV-absorbing pigments (Potts, 1996)
DNA repair (Wilson et al., 2004)
DNA protection (Potts et al., 2005)
In plants, cavitation of xylem Height <3 m, low hydraulic conductivity (Sherwin et al., 1998)
Drying too fast for induction of tolerance mechanisms In animals, contraction, construction of larval tube by Polypedilum(Kikawada et al., 2005)
In plants, signaling for induction of tolerance mechanisms via ABA (Beckett et al., 2000 Bartels and Salamini, 2001)

Plants show greater ability than animals to combine tolerance and rigidity. The leaves of desiccation-tolerant plants often curl or fold as they dry, but the stems may remain straight and change little in length(Fig. 4). This may be possible because each plant cell has its own exoskeleton, a rigid cell wall physical stress probably does not compound across groups of cells as readily in plants as in animals. Some tolerant plants do show various specialized traits that reduce the shrinkage of cells away from their walls or increase the ability of the wall to fold or bend as the cell shrinks(Table 2).

The height of desiccation-tolerant plants may be constrained by a different factor: ability to re-establish upward movement of water in stems after desiccation and rehydration (Schneider et al., 2000). Root pressure and capillary action cannot refill xylem above ∼3 m, and this is also about the maximum height of tolerant plants.

The need to lose water freely during desiccation may restrict the thickness of desiccation-tolerant organisms (Table 2). Rate of desiccation affects the survival of many tolerant organisms. Rapid drying may preclude induction of mechanisms needed for tolerance (Ricci et al., 2003 Clegg, 2005), and one function of contraction and other behavioral responses to desiccation in animals may be to slow drying (Kikawada et al.,2005). However, very slow drying may prolong the time spent at water contents just above those at which metabolism ceases, and these water contents may be particularly damaging(Berjak and Pammenter, 2001 Proctor, 2003 Walters et al., 2005). A specific mechanism to facilitate the loss of water from cells during drying may be upregulation of aquaporins that increase the permeability of membranes(Table 2).


Animal Adaptations in the Intertidal Zone

The intertidal zone is the area on a beach situated between the high tide and the low tide. This zone often includes more than one habitat, including wetlands and rocky cliffs. The intertidal zone provides habitat to a variety of animal species, such as mollusks, crustaceans, worms, some species of coral and algae. The intertidal zone can be as wide as a sandy beach several meters wide or a narrow as a steeped rocky cliff. Organisms have learned to adapt to the water level fluctuations caused by the daily tides, water turbulence, changing temperature, moisture and salinity.

Typically, an intertidal rocky shore comprises a splash zone (supratidal zone), which is the region that is repeatedly splashed by the action of waves. Along the shoreline of most beaches, the intertidal zone is usually divided into three main zones low intertidal zone, which is exposed to the atmosphere each time a low tide recedes middle intertidal zone, which is regularly exposed and flooded by the action of ocean tides and the high intertidal zone, which is only submerged under sea water by high tides however, this zone remains most of the time exposed to the land environment.

Intertidal zone stressors

The intertidal zone is continuously subjected to the influence of natural environmental factors which put the organisms thriving there at tremendous stress, so these organisms have developed ways to adapt in this harsh environment. During the course of one day, the intertidal zone is affected by two lows and two high tides, producing turbulence and drag each time a high tide recedes. During low tides, organisms are exposed to the air, higher temperatures and salinity, risking desiccation. In order to survive these stressing conditions, intertidal organisms have developed ingenious ways to cope with it.

Intertidal organisms, especially those living at the outer limits of the intertidal zone (high intertidal) are subjected to varied temperature changes. While they remain under water, the temperature may fluctuate by a few degrees however, during a low tide, temperatures may vary from freezing to hot, depending on the season. Snails and crabs feed during high tides however, during a low tide, they burrow under moist holes in the sand. Other organisms may develop either a dark or light colored shell to regulate temperature.

Many intertidal organisms will dry out or desiccate when exposed to the air and sunlight during a low tide. Snails avoid desiccation and water loss by hiding totally into their shells. Limpets live in home scars attached to hard substrates. They leave the scar for grazing and return just before the tide recedes. Some develop an outer shell or mucus membrane to shield their bodies and prevent desiccation. Some species of algae that are subjected to long periods of desiccation are able to rehydrate and recover. Barnacles and mussels attach themselves to rocks to avoid being washed away.

Some plants, such as those living in salt marshes, prevent salt uptake by secreting salt through their glands. High salinity concentrations usually occur at those locations with high salinity rates, such as intertidal pools and salt marshes. The salinity in tide pools may vary when the water contained in it is diluted by rain, affecting some fish like blennies and sculpin. Shading by some plants may slow evaporation in certain areas of the intertidal zone, reducing salinity. Sea stars, and echinoderms are intolerant to low salinities and their metabolism is unable to perform osmoregulation.

Intertidal organisms must protect from being washed away by the force of waves. Some mollusks, such as limpets, possess hard conical shells that protect them from high wave action. Sea stars have various suctioning feet used to attach themselves to hard substrates. Kelps can grow from 20-45 meters (66-148 ft.) long. They possess a holdfast with a root-like haptera, which attaches the kelp to the ocean floor, protecting it from the waves. The intertidal zone is washed everyday by the action of sea waves, and the organisms thriving there have adapted to deal with changes in temperature, moisture, turbulence, desiccation and salinity.


Unstructured Proteins Help Tardigrades Survive Desiccation

Abby Olena
Mar 16, 2017

Scanning electron micrograph of six tardigrades THOMAS BOOTHBY Hardy, microscopic animals called tardigrades, also known as water bears, can survive desiccation. Until now, it wasn&rsquot clear exactly how. The results of a study published in Molecular Cell today (March 16) suggest that proteins lacking stable 3-D structures, called tardigrade-specific intrinsically disordered proteins (TDPs), form glass-like solids that protect the animals during drying.

Other organisms achieve desiccation tolerance with a sugar called trehalose, which forms glass-like solids upon drying. For years, researchers assumed that tardigrades used trehalose, too, but many species of water bears only express small amounts of the sugar&mdashlikely not enough to confer the substance&rsquos preservative capabilities.

TDPs &ldquoseem to work by a mechanism which is similar to this sugar, trehalose,&rdquo said coauthor Thomas Boothby, a postdoc at the University of North Carolina, Chapel Hill. &ldquoIt seems like evolution has basically come up with two different ways to.

Boothby and colleagues identified a group of TDPs during a screen for tardigrade genes upregulated during desiccation. They confirmed that many of the genes’ protein products were disordered, and that these genes were expressed in three different tardigrade species, either constitutively or during drying. When the team used RNA interference (RNAi) to knock down TDP genes, the tardigrades were less able to survive desiccation.

Next, the researchers introduced TDP genes into yeast and bacteria, finding that the proteins increased desiccation tolerance in both organisms. TDPs also preserved the activity of an enzyme, lactate dehydrogenase, during drying in vitro. The authors showed that, upon desiccation, isolated TDPs transform into a glass-like substance, which also is present in—and increases survival of—both yeast that express TDPs and tardigrades during drying.

The study is “very solidly done,” biologist John Crowe of the University of California, Davis, who did not participate in the work, told The Scientist. He added that one direction for future research would be to examine the effects of TDPs on cell membranes.

“It’s been well known for some time that polymers like this can prevent fusion between membranes during drying, but they don’t preserve them completely,” Crowe said. “Small molecules like trehalose or glucose, or some other small sugar, are required in addition. It may well be that the small amount of trehalose that’s found in tardigrades in conjunction with those proteins may do the job. You might need both.”

According to Boothby, another open question is whether tardigrade species other than the three examined in this study use a similar mechanism to protect against desiccation. There are more than 1,200 tardigrade species, divided into two classes.

“It’s going to be really instructive if and when we can start looking at differences between those classes,” said Carl Johansson, an instructor at Fresno City College in California who was not involved in the work.

Probing how TDPs function at a molecular level to protect the animals from desiccation could have applications beyond water bears. “This represents the first step that could be used to improve the capability of other organisms to desiccate in the future,” said coauthor Lorena Rebecchi of the University of Modena and Reggio Emilia in Italy. Rebecchi explained that learning more about tardigrade proteins could eventually enable researchers to safely desiccate plants and other animals.

“People don’t know about tardigrades, but they are very important,” she said. “They have a lot of biological secrets that could be used to improve the quality of human life.”


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